Installation guide

Network Infrastructure for EtherNet/IP™
6-70
Infrastructure Application Scenarios
Confirm that the total
unwanted multicast traffic value is less than each devices’ maximum unwanted
multicast traffic rate. If it is greater, add managed switches. Adding managed switches reduces the
multicast domain as shown in Figure 6-3.
Figure 6-3 Use Managed Switches to Reduce the Size of a Multicast Domain.
This is also a key concept for end users who may be interconnecting multiple OEM machines from one or
more vendors. To minimize application timing problems and maximize determinism, separate the traffic
from the different machines with managed switches.
Consider future expansion needs.
In the future, before connecting any additional devices to the unmanaged switches, first determine if the
unwanted muticast traffic load of the existing installation (as well as the added device) can withstand the
added device’s traffic. Failure to do this runs the risk of adding one device that shuts down the system. It
is reccommended that any new sections or expansions be connected into a managed switch to add IGMP
snooping capabilities.
Alternative traffic management approaches.
In cases when the prefered calculation approach is not possible and the maximum unwanted multicast
traffic rates cannont be obtained from the device vendors, there are three options:
1. Use all managed switches (with IGMP snooping). This is the best alternative and the
most conservative approach to system design because it keeps traffic and application
timing issues to a minimum.
2. Test the configuration during the design phase. Pre-test each multicast domain
(unmanged switch section) to confirm proper operation using the actual application
configuration and controller/scanner RPI value. Be sure to allow time to add managed
switches to the system design if they are needed.
3. Reconfigure devices to use unicast messages. Some devices may have a user-
selectable option to produce implicit (I/O) messages using unicast messaging instead of